Refrigeration



Dec. 6, 1938. r Y J. G. BERGDOLL 3 2,139,297

' REFRIGERATION Filed March 6, 1937 2 Sheets-Sheet 1 DIRECTION OF 3AIRFLOW TH ERMAL EXPANSION VALVL SUCT'I ON L] N E REcE1vzK- Counnnsmz.Lm m mu:

Fi mm Y 5 3-34.11, U" 370/ 590- YFRESHAIR so I 414 LTLW mm i 3h ventor J28w ssw I I I 25 mom EXPANSIONVALVE u attorneys J. G. BERGDOLLREFRIGERATION Dec; 6, 1938.

Filed March 6, 1957 2 Sheets-Sheet 2 DIRECTION OF AIR. FLOW FROMDISTRIBUTO 3nnentor DIRECTION OFAIK'FLOW attornegs Patented 6, 1938REFRIGERATION John G. Bergdoll, York, Pa., assignor to York IceMachinery Corporation, York, Pa., a corporation of Delaware ApplicationMarch 6, 1937, Serial No. 129,475 I 13 Claims.

This invention relates to refrigeration andparticularly to the coolingof a flowing stream of fluid by a refrigerative evaporator fed by athermally controlled expansion valve. The invention will be described asapplied to the cooling of a stream of air, without however implying'theexclusion of other gases or even liquids.

The fact that an evaporator converts the sensi- 'ble heat abstractedfrom the air into latent heat, leads to special efiects which must beappreciated if the invention is to be understood.

Consider two streams of liquid, one hot the other cold, exchangingsensible heat through a surface exchanger. ,As is well known, concurrentl5 flow permits both liquids to approach a mean temperature, whereascounterflow permits each liquid to approach the entrance temperature ofthe other. Obviously counterflow gives a more nearly uniform temperaturedifference and consequently the most effective interchange where onlysensible heat is exchanged.

Now consider an-evaporator cooler cooling a stream of air. Thetemperature ,of the refrigerant in the evaporator is a function of thepressure; In an evaporator the pressure is never uniform, for flowresistance in even a well designed evaporator of the finned tube typecauses a pressure drop varying from 2 to 6 lbs. per square inch frominlet to outlet, depending on operating conditions. The temperature ofsuccessive points in the evaporator must fall correspondingly.Accessions of heat evaporate liquid, but so long as liquid is present donot increase temperature. The pressure alone controls evaporatortemperature.

Because evaporator temperature falls in the direction of refrigerantflow, concurrent how (with respect to the air stream) gives results inan evaporator somewhat analogous to those secured by counterflow in thecase of simple exchange of sensible heat. Since liquid refrigerantenters the warmer end of the evaporator, evaporation and flashgeneration of gas are intense. Consequently rapid flow of refrigerantthrough the evaporator is secured and greatly intensifies heat transfer.

The above considerations imply that 'an evaporator fed .by a thermallycontrolled expansion valve and cooling a stream of air should bearranged for concurrent flow and so arranged would carry a.refrigerative' load near the theoretical limit of the coil. Suchresultshave not been attained in practice and the discovery of the reaso is thebasis of the present invention.

With concurrent flow, refrigerant leaves the cold end of the coil at apoint where the air is also cool and can supply little heat to establishthe superheat demanded by the thermostatic expansion valve. Hence anabnormally large portion of the evaporator is used to supply superheatand is, in consequence, relatively inefiective to refrigerate. If a.more effective superheater can be arranged the coil can be more nearlyflooded and theoretical performance-can be more nearly approached.

According to the invention I divide the evaporator into two sections, asmall superheater section with which the air first exchanges heat and bywhich the air is somewhat cooled, and a larger main refrigeratingsection with which the air next exchanges heat and by which the majortemperature reduction is eilected.

Refrigerant from the expansion valve enters the main refrigerativesection and flows therethrough in concurrent flow relation with the air.Refrigerant discharging from the main section is then passed through thesuperheater section, preferably, but not necessarily in counterflowrelation to the air. Since the superheater section receives heat fromthe warmest (entering) air, it is highly effective and need form only asmall fraction of the entire evaporator.

Such an arrangement gives more steady operation, better thermal control,and larger cooling capacity than can be had byeither concurrent flowalone or counter flow alone. The main section can be operated nearlyflooded, the refrigerant flow is rapid and in consequence the totalevaporator surface may be made smaller in comparison with similarevaporators heretofore required for comparable loads. The economicseffected in space and cost of apparatus are substantial.

In modern'comfort coolers using refrigerants such as F12 or Freon (tradenames) it has been found desirable to use a plurality of evaporatorunits connected in parallel and fed by a single thermal expansion valvethrough a turbulent mixer or distributer head which serves to deliveruniform mixtures of liquid and vapor to the various units. The inventionwill be described as r so embodied, without implying the necessary useof multiple units. v 1

In the drawings:

Fig. 1 is a diagram, partly in elevation and partly in section showing atypical refrigerating circuit. The direction of air flow is indicated byan arrow and related legend. The duct is broken away to show theevaporator structure.

. Fig. 2 is a perspective view of thetube forming the two sections ofone unit of the evaporator in Fig. 1. The fins are omitted so that thepath of refrigerant can be traced.

Fig. 3 is a plan view of the distributer head.

Fig. 4 is an axial section therethrough.

Fig. '5 illustrates a modification in which the fins on the main andsuperheater sections are distinct to minimize heat transfer between thetwo sections.

Fig. 6 illustrates a further modification.

Referring to Fig. 1, the suction line is indicated at 6 and leads to thecompressor 1. The compressor is driven by motor 8 through a belt 9 anddischarges through high pressure line I I into a combined condenser andreceiver 12. The condenser chosen for illustration is water cooled butthis is immaterial. From receiver 12 liquid line I3 leads to theexpansionvalve, whose body appears at i4.

The valve proper I5 is loaded in a closing direction by spring l6 whosestress is adjustable by turning screw II. The valve is shifted toregulate superheat in the suction line by diaphragm l8 subject to theopposing effects of suction temperature and suction pressure. The motordiaphragm I8 is urged in a valve opening direction by vapor pressuredeveloped in thermostatic bulb l9 by rising temperature and communicatedto the space above the diaphragm by pipe 2|. The lower face of thediaphragm is subject to suction pressure communicated by pipe 22. BulbI9 is on the suction line and pipe 22 is connected adjacent the bulb, sothat diaphragm i8 responds to the pressure-temperature relation atsubstantially a single point. A packing gland 23 protects the lower faceof the diaphragm from the through the evaporator by appropriateadjustment of spring l6.

From body 14 expansion line 24 leads to the distributer head whose bodyis indicated at 25. Pipe 24 leads to nozzle 26 (see Figs. 3 and 4) whichdischarges in the center of toric turbulence chamber 21, producingtherein violent rotary turbulence. Four symmetrically arranged tubularbranches 28 lead uniform mixtures of liquid and vapor from chamber 21 tofour evaporator units.

The major pressure reduction occurs at valve [5 but the tubes 28 ortheir entrance orifices or both may be arranged to provide suchthrottling as may be advisable to balance the delivery to the fourevaporator units. There is also some pressure drop through theevaporator.

While I show four units any suitable number may be used. The circuit soar described is largely conventional and no novelty is here claimed forit. Equivalents may be substituted.

The invention here claimed resides in the evaporator, particularly theconnections of and flow path through each unit with reference to thepath of air in contact with the unit. The units are essentiallyidentical and a description of one will suflice.

The units extend horizontally one above the other. Each tube 28 connectsat 29 with the evaporator tube 3|. This zig-zags upward in a verticalplane for three passes, offsets to the right, then zig-zags downward forthree passes, again offsets to the right and so on through six tiers ofpasses to 32. Stated directions refer to Figs. 1 and 2 and the number ofpasses is subject to variation. The tube 3| from 29 to 32 forms the mainevaporator. From 32 the refrigerant is led back to 33 which is theentrance to the superheating unit. This is formed as a continuation oftube 3|, and zig-zags upward three passes, offsets to the left, zig-zagsdownward three passes and enters suction manifold 35 at 34. Suction line6 leads from manifold 35 at about mid-height and the filler piece 36 isplaced in the lower half of the manifold to accelerate flow there andinhibit the accumulation of liquid. Such accumulation, if permitted tooccur would retard flow through the lower units, and would produce afalse temperature condition at the thermal bulb as compared with theactual gas temperature leaving the coil circuits In Fig. 1 all fourunits including both sections of each unit are provided with a series ofparallel plate fins, the first one of which appears at 31. These may beof any known type and either flat or corrugated. The entering air may befresh air, recirculated air or a mixture of the two. The air flow isdirected in contact with the evaporator by a duct 38 and is induced by afan 39 or other suitable means.

In Fig. 5, which shows a modification, two distinct sets of fins areused 318 on the superh'eater section and 31m on the main evaporatorsection. This thermal segregation of the sections somewhat improvesperformance, but the improvement is not great enough to justify theextra cost in all cases.

In Fig. 5, as in Fig. 1, there is a distinct superheater section foreach main section, but this need not be so, for all the main sectionsmay deliver to a single superheater. Fig. 6 shows this arrangement aswell as other optional features.

In Fig. 6 distributer head 25a is fed by an expansion valve (not shown)identical with the expansion valve 14 of Fig. 1. Thermal bulb Na andpressure connection 22a control this valve exactly as the similarlynumbered parts in Fig. 1 control expansion valve I4. Branches 28a leadfrom head 25ato four main units the entrance connection being at 29a andthe exit connection at 32a which leads to manifold 30. Manifold 30 isconnected by pipe 33a to a single finned superheater coil 34a from whichthe suction line So. leads. Fins 31a, duct 38a and fan 39a correspond toparts 31, 38 and 39 of Fig. 1.

In Fig. 6 fresh air entering through adjustable louvers 4] alonecontacts superheater coil 34a. This is the warmest air available. Afterwarming coil 34a, this air and recirculated air fed back from theconditioned space through return air duct 42 and adjustable louvers 43,flow together over the main coils in concurrent flow relation with therefrigerant.

In any case illustrated the air flow is such that the air first passesin heat exchanging relation with the superheater section (or sections)and then in heat exchanging relation with the main evaporator section(or sections) this last in concurrent flow relation with therefrigerant. Such direction as to Figs. 1, 5 and 6 is from left to rightas indicated by the arrows and legends on these figures;

lll

arsaaov Some idea of the advantage of the described arrangement can behad by considering a typical case. Entering air at 80, F. cooled-to 6%"h. at discharge with a suction pressure of 3d lbs corresponding to 40F., can be assumed as typical. With simple concurrent flow, there wouldbe a temperature diflerence of only to impart a 10 superheat. By thepresent arrangement there is a 40 temperature difference to impart thesuperheat, yet substantially the entire advantage of concurrent flow isretained. its a consequence the evaporator may be more heavily loadedand operates more steadily and eiflciently.

Iii

What is claimed is,- l. The method of cooling a stream of fluid hy flowin heat exchanging relation withan evaporator which comprises passingthe fluid in heat.

exchanging relation with a refrigerant superat a pressure lower than thepressure at which said liquid r refrigerant is supplied; and varying therate of such supply of liquid refrigerant in relation to thedifferential between a force pro portional to evaporator pressure and aforce proportional to the temperature of said withdrawn 0 refrigerant.

2. The method-of cooling a stream of fluid by flow in heat exchangingrelation with an evaporator which comprises passing the fluid in heat aexchanging relation with a refrigerant superheating section and then inheat exchanging relation with a main refrigerant evaporating section ofan evaporator while supplying volatile liquid refrigerant under pressureto the said main section, directing the refrigerant therethrough inconcurrent flow relation relatively to the fluid stream and thencedirecting it through said superheating section in counterflow relationrelatively to said fluid stream; withdrawing superheated refrigerantvapor from said superheating section at'a pressure lower than thepressure at which said liquid refrigerant is supplied; and

varying the rate of such supply of liquid refrlgerant in relation to thediflerential between a force proportional to evaporatorpressiu'e and aforce proportional to the temperature of said withdrawn refrigerant.

, d. The method of cooling a stream of fluidity flow in heat exchangingrelation with an evaporator which comprlsespassing the fluid in heat"exchanging relation with a refrigerant superheating section and then inheat exchanging relatlon with a main refrigerant evaporating sec-'- tionof an evaporator while supplying volatile liquid refrigerant underpressure to the said main section, directing the refrigeranttherethrough-ln concurrent flow relation relatively to the fluid steamand thence directing it through said superheatlng section; withdrawingsuperheated refrigerant vapor from said superheatlng section at apressure lower than the pressure at whichsald liquid refrigerant issupplied;- and varying the rate of supply of liquid refrigerant inrelation to the degree of superheat of the withdrawn refrigerant, tomaintain said .superheat substantially constant. i

d. The method of cooling a stream of fluid by how in heat eirchi i itrelation with an evapoirator which comprises passing the fluid in heatexchanging relation with a refrigerant superheating section and then inheat exchanging relation with a main refrigerant evaporating section ofan evaporator while supplying volatile liouid refrigerant under pressureto the said main section, directing the refrigerant therethrough inconcurrent flow relation relatively to the fluid stream and thencedirecting it through said superheating section in counter-flow relationrelatively to said fluid stream; withdrawing superheated refrigerantvapor from said super-heating section at a pressure lower than thepressure at'which said liquid refrigerant is supplied; and varying therate of supply of liquid refrigerant in relation to thedegree ofsuperheat of the withdrawn refrigerant, to maintain said superheatsubstantially constant.

= d. The method of cooling a flluid by evaporation of a volatilerefrigerant in an evaporative surface cooler, which comprisescirculating the fluid in heat exchanging contact with such cooler,performing the major portion of the cooling of the fluid hy evaporationof liquid refrigerant to a suitstantiaily saturated vapor condition in amajor I portion of said cooler with respect to which portion the how offluid and refrigerant are con current, imparting superheat to thesaturated vapor so produced in a minor portion of said coolor with whichfluid substantially unauected by exchange of heat with said majorportion err changes heat, and varying the rate of supply of liquidrefrigerant to said evaporator surface cool or in relation to thediderential between a force proportional to evaporator pressure and aforce proportional to the temperature of said withdrawn refrigerant,

6. The method of cooling a fluid icy evaporation of a volatilerefrigerant in an evaporative surface cooler, which comprisescirculating the fluid in heat exchanging contact with such cooler,

performing the major portion of the cooling of V the fluid byevaporation of liquid refrigerant to a substantially saturated vaporcondition in a major portion of said cooler with respect to which portion the flow of fluid and refrigerant are concurrent, impartingsuperheat to the saturated vapor soproduced in a minor portion'of saidcooler with which fluid suhstantially unadected hy euchange of heat withsaid major portion exchanges heat, and varying the supply of volatilerefrlger ant to said surface cooler in relation to the degree ofsuperheat of refrigerant leaving said minor Y portion to maintain saidsuperheat substantially constant i. 'lihe method of cooling a fluid hyevaporation of a volatile refrigerant in an evaporative surface cooler,which comprises circulating the fluid in heat exchanging contact withsuch cooler, performing the major portionof the cooling of the fluid icyevaporation of volatile refrigerant to a suhstantialiy saturated vaporcondition, in a plurality of parallel-flow streams in a major portion ofsaid cooler with respect, to which portion the flow of fluidand of theparallel-flow refrigerant streams are concurrent, imparting superheat tothe saturated vapor so produced in a minor ponunaflected by the majorportion of said cooler ex changes heat, and varying the supplyofvolatile tion of said cooler with whlch fluid substantially Irefrigerant to said surface cooler in relation to the degree ofsuperheat of refrigerant leaving said minor portion. g

8. The method of cooling a fluid by evaporation of a volatilerefrigerant in an evaporative surface cooler, which comprisescirculating the fluid in heat exchanging contact'with such cooler,

performing the major portion of the cooling of the fluid by evaporationof volatile refrigerant to a substantially saturated vapor condition ina plurality of parallel-flow streams in a major portion of said coolerwith respect to which portion the flow of fluid and of the parallel-flowrefrigerant streams are concurrent, imparting superheat to the saturatedvapor so produced by heat exchange withthe warmest available fluidapproaching said surface cooler, and varying the supply of volatilerefrigerant to said surface cooler in relation to the degree ofsuperheat of refrigerant leaving said minor portion.

9. The combination of an evaporator comprising a minor superheatingportion and a major cooling portion; means for circulating a fluid firstover said superheating portion and then over said main cooling portion;meansforgsupplying volaover said super-heating portion and then oversaid main cooling portion; means for supplying volatile refrigerant tosaid main cooling portion and causing it to flow therethrough inconcurrentflow relation with said fluid, then to flow throughsaidsuperheating portionin counterflow relation with refrigerant.

said fluid; and a thermostatic expansion valve controlling said supplyof refrigerant, said thermostatic valve being arranged to be controlledat least in part by the temperature of refrigerant leaving saidsuperheating portion.

11. The combination deflned in claim 9, in ,which the main sectioncomprises a plurality of units through which the refrigerant flows inparallel'and the superheater section comprises a corresponding pluralityof unitsthrough which refrigerant evaporated in the main unit flows inparallel.

12. The combination defined in claim 9, in which the main evaporatorcomprises a plurality of units through which the refrigerant flows in'parallel and the superheater is'a single unit to which all the units ofthe main section deliver 13. The combination of an evaporator comprisingaminor superheating portion and a major cooling portion; means forcirculating a fluid to be cooled in heat exchanging relation with saidevaporator; means for supplying volatile refrigexam; to said maincooling portion and causing it to flow therethrough and then throughsaid superheating portion; means controlling the supply of refrigerantto said evaporator; means responsive-to the condition of refrigerantleaving said superheating portion and serving to control said supplycontrolling means; and means controlling the flow of fluid to be cooledand serving to direct the warmest available fluid into heatexchangingrelation with.said superheating portion and to cause the flow relationwith the volatile refrigerant in said main cooling portion.

J OHN G. BERGDOLL.

fl uid to flowin concurrent

